It is often desirable to provide termination resistors or other programmable terminations for input and output signal lines in an integrated circuit. For example, termination resistors may be incorporated into the integrated circuit in order to match input and output impedances of respective receiver and driver circuitry of the integrated circuit to impedances of corresponding circuitry or traces on an associated circuit board. As is well known, impedance matching of this type is beneficial in that it reduces signal reflections and associated effects such as ringing, loss, standing waves, etc. Termination resistors that are incorporated into a given integrated circuit are commonly referred to as “on-chip” termination resistors.
A significant drawback of conventional on-chip termination resistors is that such resistors and their associated control circuitry generally fail to provide a sufficient level of programmability. For example, the conventional techniques may require that multiple input or output pads in a given group of pads all be biased from the same supply voltage terminal and have the same value of termination resistance. Moreover, such techniques may require that one or two pads in each group of pads be used for providing references for control of termination resistance, which reduces the number of pads which can be used for input or output signal lines.
As a result, the conventional techniques may unduly limit circuit performance or restrict circuit configuration flexibility in certain integrated circuit applications, such as, for example, those involving field programmable gate array (FPGAs), field programmable system chips (FPSCs), or application-specific integrated circuits (ASICs).
It is therefore apparent that a need exists for improved techniques for providing programmable terminations in an integrated circuit or other electronic circuit.